1. Field of the Invention
The present invention relates to a high-voltage generator for generating a high voltage transmitted to an accelerator for accelerating a charged particle, such as an ion and an electron, for example. Particularly, the present invention relates to a high-voltage generator that can prevent electrical circuit parts used therefor from being damaged by an electrical discharge and that can be reduced in size. The present invention further relates to an accelerator using the above-described high-voltage generator.
2. Description of the Related Art
In known high-voltage generators used for the accelerator for accelerating the charged particles, such as the ion and the electron, metal hoops (conductive annular members) disclosed in Japanese Unexamined Patent Application Publication No. 6-176891, for example, are provided outside a high-voltage circuit including a capacitor, a diode (rectifier element), and so forth. The use of the metal hoops allows for reducing the nonuniformity of an electric field formed by the high-voltage circuit, thereby reducing the occurrence of an electrical discharge.
In general, a Cockcroft-Walton circuit (hereinafter referred to as a CW circuit) is used in the known high-voltage generators. FIG. 5 shows a high-voltage generator 50 using a CW circuit 51. The CW circuit 51 includes a plurality of booster circuits 54 connected to each other in multiple stages, whereby a double-voltage circuit is formed. In this drawing, six booster circuits are provided in the CW circuit 51. Each of the booster circuit 54 includes diodes 52, capacitors 53, and so forth. As an input voltage is sequentially transmitted from the low-voltage side (the external-voltage input side) to the high-voltage side (an upward direction in FIG. 5), the input voltage is gradually boosted. Subsequently, a large potential difference is generated between a low-voltage part 56 and a high-voltage part 57 of the CW circuit 51, which makes an electric field around the CW circuit 51 non-uniform. Further, because of the non-uniform electric field, peripheral elements or the like around the CW circuit 51 are easily charged, which increases the possibility of the electrical-discharge occurrence between the peripheral elements, or the peripheral elements and electric circuit parts including the diodes 52, the capacitors 53, and so forth. For reducing the electrical-charge occurrence, a plurality of substantially annular metal hoops 58 is provided outside and around the CW circuit 51. The metal hoops 58 are provided at predetermined positions, so as to correspond to the booster circuits 54 with predetermined distances therebetween. Subsequently, the electric field around the CW circuit 51 becomes substantially uniform, which reduces the electrical-discharge occurrence caused by the non-uniform electric field. FIG. 6 is a schematic diagram of the known high-voltage generator including the metal hoops 58 and FIG. 7 is a sectional view taken along the line VII—VII.
In the case of a high-voltage power supply disclosed in Japanese Unexamined Patent Application Publication No. 7-312300, substrates connected to multistage booster circuits of a CW circuit are molded of a flexible insulation resin. Subsequently, the occurrence of an electrical discharge in the CW circuit reduces. Further, each of distances between the substrates decreases, whereby the high-voltage power supply is miniaturized.
In the known accelerators for accelerating the ion or the electron, a high-voltage circuit for transmitting a high voltage to an acceleration unit is provided outside an acceleration tube, which reduces spaces between the elements of the accelerator. However, since a predetermined distance must be provided between the acceleration tube and a high-voltage power supply for reducing the electrical-discharge occurrence, the proximity of the acceleration tube and the high-voltage power supply decreases, which hampers miniaturization of the high-voltage power supply.
More specifically, the above-described Cockcroft-Walton circuit, that is, a Cockcroft-Walton high-voltage power supply is often used, as the high-voltage circuit of the above-described accelerator. Usually, both the voltage of the Cockcroft-Walton high-voltage power supply and that of the acceleration tube for accelerating an ion and/or an electron by distributing the boosted potential are high. Further, an electrical discharge is likely to occur, where the proximity of the Cockcroft-Walton high-voltage power supply and the acceleration tube is increased without suitable preparation. Therefore, the high-voltage power supply and the acceleration power supply must be provided with a predetermined distance therebetween, which hampers miniaturization of the entire accelerator.
Although the known metal hoops disclosed in Japanese Unexamined Patent Application Publication No. 6-176891 can reduce the electrical discharge in the high-voltage circuit, such as the above-described CW circuit or the like, they are not sufficient enough for completely eliminating the electrical discharge. Accordingly, it was not possible to completely prevent the electric circuit parts used for the high-voltage circuit from being damaged or burnt by the electrical discharge. However, where distances between the electric circuit parts, or the peripheral elements and the electric circuit parts are increased, the insulation effect is enhanced and the electrical-discharge occurrence decreases. In that case, though the electrical circuit parts are prevented from being damaged and/or burnt, the high-voltage generator increases in size. Further, since voltages transmitted to the accelerator or the like have become increasingly high in recent years, so as to increase the energy of a charged particle such as an ion, the above-described electric circuit parts have become more likely to be damaged and/or burnt by an electrical discharge.
Where each of the substrates on which the booster circuits are formed is molded of the flexible resin, as in the case of the high-voltage power supply disclosed in Japanese Unexamined Patent Application Publication No. 7-312300, the substrates are prevented from being damaged and/or burnt by an electrical discharge. However, the cost and time required for the molding is so high that the use of the above-described high-voltage power supply is not economical.